Dynamics of plasmid-mediated niche invasion, immunity to invasion, and pheromone-inducible conjugation in the murine gastrointestinal tract

Microbial communities provide protection to their hosts by resisting pathogenic invasion. Microbial residents of a host often exclude subsequent colonizers, but this protection is not well understood. The Enterococcus faecalis plasmid pCF10, whose conjugative transfer functions are induced by a peptide pheromone, efficiently transfers in the intestinal tract of mice. Here we show that an invading donor strain established in the gastrointestinal tract of mice harboring resident recipients, resulting in a stable, mixed population comprised of approximately 10% donors and 90% recipients. We also show that the plasmid-encoded surface protein PrgB (Aggregation Substance), enhanced donor invasion of resident recipients, and resistance of resident donors to invasion by recipients. Imaging of the gastrointestinal mucosa of mice infected with differentially labeled recipients and donors revealed pheromone induction within microcolonies harboring both strains in close proximity, suggesting that adherent microcolonies on the mucosal surface of the intestine comprise an important niche for cell-cell signaling and plasmid transfer.

The input inocula were prepared by the Dunny lab and supplied to the Mayo lab as frozen inocula. We did not blind the samples for the Mayo lab because only a limited number of personnel with the expertise to understand and carry out the experiments were available, and the selective plate media needed for each experiment were unuique for each experiment. As a confirmation of the emueration data and the quality of the bacterial inocula, both labs independently, directly plated and enumerated samples of each culture aliquot used in mice.
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Mycoplasma contamination
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March 2021
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Gnotobiotic Swiss Webster mice bred in the Mayo Germ-free mouse facility were used in this study. Animals and their care are described in detail in the Methods section of the manuscript.

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March 2021
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